PROBLEM TO BE SOLVED: To automatically switch a flow passage of a stop cock, and detect a position of a rotation angle.SOLUTION: The stop cock driving device comprises: a cylindrical cam 101 on the outer periphery of which a loop-like groove 102 is formed and that can rotate in normal and reverse directions； two driving pins 103, 104 that are respectively arranged in the groove 102 and can linearly move forward and backward； a three-way stop cock 403a connected to the cylindrical cam 101 and switching a flow passage； and a control part 110 for switching the flow passage of the three-way stop cock 403a by linearly moving the two driving pins 103, 104 forward and backward in a direction along an extension direction of the cylindrical cam 101 and rotating the cylindrical cam 101 to a center C of rotation in a normal or reverse direction.【課題】活栓の流路の自動切り替え、および回転角度の位置を検出する。【解決手段】外周面にループ状の溝１０２が形成され、正逆方向に回転自在な円筒カム１０１と、それぞれ溝１０２に配置され、直線往復運動可能な２つの駆動ピン１０３，１０４と、円筒カム１０１に接続され、流路を切り替える三方活栓４０３ａと、２つの駆動ピン１０３，１０４を円筒カム１０１の延在方向に沿った方向に直線往復運動させて、円筒カム１０１をその回転の中心Ｃに対して正または逆方向に回転させることで三方活栓４０３ａの上記流路を切り替える制御部１１０と、を有している。【選択図】図１
